How to return existing matching record for Django CreateView

Question

I use a regular generic.edit.CreateView of Django to create an object according to user input. The MyModel has an UniqueConstrait so the creation would fail if the new object happens to match an existing one.

However, instead of telling users that creation fails due to duplicate records, I would like to simply return the existing object since this is what users want. I tried to override

    def save(self, commit=True):
        return MyModel.get_or_create(value=self.cleaned_data['value'])[0]

but this does not work because form._post_clean will call form.instance.full_clean with its default validate_constraints=True, so an error will return during form validation.

Essentially I am looking for a GetOrCreateView but I am not sure what is a clean way to achieve this (other than maybe overriding form._full_clean). Note that I am not looking for a UpdateView because we do not know in advance which existing object will be returned.

Edit: After struggling with the validation issue for a very long time, I finally abandoned CreateView and resorted to a simpler FormView. The FormView will simply get all the user input I need, before calling get_or_create(form.cleaned_data[...]) in form_valid(self, form).

What's wrong with .exist()? I think you can use it by doing: existing_object = MyModel.objects.get(id=pk).exist() then you can pass an error message. — Adamu Abdulkarim Dee
– Adamu Abdulkarim Dee, Commented May 24, 2023 at 22:09
I do not have a pk to get the existing_object. The scenario is that the user is creating an object by entering a name in a form backed by a CreateView, the name happens to clash with an existing object so the CreateView is supposed to return an existing object matching the user's input, instead of creating a new one. — user2283347
– user2283347, Commented May 26, 2023 at 15:51

Adamu Abdulkarim Dee · Accepted Answer · 2023-05-28 20:57:45Z

0

To achieve the behavior you described, where instead of raising an error for duplicate records, you want to return the existing object, Here's an example of how you can implement it:

class CreateObjectOfMyModel(CreateView):
    model = MyModel
    fields = ['value']

    def get_form(self, form_class=None): 
        form = super().get_form(form_class) 
        value = form.data.get('value')
        form.fields['value'].queryset = MyModel.objects.filter(value=value)
        return form

The get_form method is overridden in this class base view, It calls the get_form method using super().get_form(form_class) to get the base form object. Then the value field of the form to filter out duplicate records, I have also added a line to retrieve the entered value from the form data using form.data.get('value'). I hope it works.

edited May 28, 2023 at 20:57

answered May 27, 2023 at 12:08

Adamu Abdulkarim Dee

3056 silver badges19 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Ezon Zhao Over a year ago

I would argue that form_valid will never be called if there exists duplicate record, since a unique validation error will be raised in form validation and thus form_invalid gets called instead. Instead, one should override post method.

Adamu Abdulkarim Dee Over a year ago

You're correct. The form_invalid method will be called instead of form_valid. Check my answer again.

user2283347 Over a year ago

This will not work either because is_valid() will call self.errors, self.full_clean(), self._post_clean(), self.instance.full_clean() and return False due to the constraint on the model. I think the root problem is that django (4.2) allows bypassing validate_unique, but does not allow bypassing validate_constraints of models.base.Model.full_clean(), so form validation will always fail in this particular example (unless _post_clean is overriden).

Adamu Abdulkarim Dee Over a year ago

You're correct in your analysis. The code I provided will not work as intended due to the way Django's form validation Check my answer again, I hope it would work.

user2283347 Over a year ago

Thanks. Your solution might work for simple cases but in my real application user inputs from multiple fields need to go through a series of clean_ calls before they are used to create an object, so it is awkward to override get_form this way.

|

Collectives™ on Stack Overflow

How to return existing matching record for Django CreateView

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related